The Hellenistic Stoics defend a striking combination of claims within their physics, some of which appear to be in tension with others. First, they argue that only bodies can be causes, and all processes and conditions in the natural world result from bodies making contact with each other. However, they also maintain that an omnipresent God exists, and he crafts the world to be as good as possible. Thus, God turns out to be a body, according to the Stoics: he is physically present in the cosmos, and he makes contact with other bodies to carry out his plans. But what kind of body could perform these wide-ranging, divine functions?
Next, the Stoics maintain that the world is constituted by a single, continuous body, which they sometimes call “primary matter”. This body is eternal, static in mass, and formless in its own nature. However, they also assert that the entire world is an animal, and it undergoes dynamic processes of change and growth. Furthermore, this cosmic animal is composed of innumerable other dynamic parts—including human beings, non-rational animals, plants, and inanimate objects. Thus, on the one hand, the world is stable and completely uniform; on the other hand, it is dynamic and constituted by a variety of objects and processes. How are these claims compatible?
Finally, the Stoics argue that there are four types of incorporeal entities—place, time, void, and “sayables” or lekta. While these incorporeals cannot cause anything, they are metaphysically independent and essential to a complete explanation of the natural world. On the other hand, the Stoics sometimes seem to maintain that bodies are more fundamental than these incorporeals. They say that only bodies exist, while incorporeals merely subsist or obtain. Are the incorporeals meant to be dependent on bodies or less real than bodies, or is this a misinterpretation of Stoic metaphysics?
In my work, I investigate these areas of Stoic natural philosophy, as it developed under the first three leaders of the school—Zeno, Cleanthes, and Chrysippus. Despite the popularity of the Stoic school in the Hellenistic period, no complete original treatises written by these three philosophers have survived to the present day. Thus, in my work, I examine the second-hand evidence for their views, which spans the first century BCE to the fifth century CE, including sources such as Cicero, Diogenes Laertius, Stobaeus, Philo of Alexandria, and Plutarch, among many others.
As a fellow, I am exploring how the Stoics and these sources use certain key terms in Stoic natural philosophy—“substance” (οὐσία), “matter” (ὕλη), “god” (θεός), “reason” (λόγος), “body” (σῶμα), “soul” (ψυχή), “subsist” (ὑφίστασθαι), and “obtain” (ὑπάρχειν), among others. Because the sources for Stoicism often use these terms in different, incompatible ways, how the Stoics employed these concepts becomes unclear. In my research, I identify the different senses of these words in the evidence, explain how these different senses generate interpretive puzzles, and then attempt to untangle the Stoics’ views from those puzzles. By doing this, I dissolve some of the apparent tensions in Stoics physics, while explaining and motivating the philosophical underpinnings of others.
Ian Hensley is an Assistant Professor in the Department of Philosophy and Humanities at East Tennessee State University. He has previously held teaching positions at Cornell University, the University of Illinois, and the University of Missouri. He has a Ph.D. in Philosophy from Cornell University. His main area of research is natural philosophy in ancient Greece and Rome and its connections to contemporary philosophical problems in metaphysics and philosophy of mind. He has recently published articles on the Hellenistic Stoics’ theories of the principles of nature, cosmogony, and pneuma.